Then he would have two days to himself before coming back on duty.

I couldn't tell if he was on or off duty.

These men were on duty 24 hours a day, seven days a week.

I have been on duty for only a short time.

Four of them will be back on duty in a week.

You'll have to go back on duty in three days.

He's not on duty so he and his wife must both be out.

He spent half of the 1971 season on military duty.

Why do they always show up when I'm on duty?

He/she is on duty for several hours in each school every week.